This invention relates to diesel fuel filters and more particularly to a fuel filter which includes heater means therein for elevating the temperature of the fuel to prevent buildup of residues and subsequent dogging of the fuel system.
The application of heater devices to diesel fuel filters has become accepted in the field because of the successful results obtained and the fact that much wider temperature ranges can be accommodated, which had previously introduced problems of dogging and plugging of the filters. While initially heaters were adapted to preexisting filter devices, it has now become commonplace to incorporate the heater as an integral part of the filter assembly and to achieve an efficient heat transfer with the fuel being passed to the filter element.
In particular, heater elements have been applied to the spin-on type of fuel filter wherein it is desired not only to obtain an efficient heat transfer relationship, but also to provide an efficient housing structure which can be incorporated safely into an engine compartment and still provide relatively free access for filter changes, maintenance and the like. Particular attention has been paid in such devices to the retention of a quantity of fuel in the filter head and/or the heater element so that when the filter element is exchanged there is not an excessive spillage of fuel. An alternate scheme is to provide means for efficiently draining the filter casing or cartridge prior to removal of the spin-on element so as to avoid or minimize the fuel spillage problem.
One device of this type is shown in U.S. Pat. No. 4,387,691 wherein a particular form of heater structure is employed in the filter head of a filter assembly which includes a spin-on type of filter element. Particular attention is paid in this disclosure to the routing of fluids through the heater structure and the filter medium so as to achieve an efficient and advantageous heat transfer relationship.
A similar arrangement of diesel fuel heater is shown in U.S. Pat. No. 4,406,785 wherein a plurality of PTC fuel heater elements are disposed on a conducive plate and located within the filter head of a fuel filter assembly to achieve the heat transfer relationship. In this form of apparatus, a circuitous path of travel for fluid flow through the heater element is provided which is on the order of 360.degree. in angular length and the heater is directly operative in the fuel path.
Still another form of prior art device is shown in U.S. Pat. No. 4,596,224 wherein a separate insulative housing is provided for the fuel heater which housing is disposed between the filter head and the spin-on element and in which, again, a circuitous path of travel for the fluid flow is provided.
A more recent disclosure is made in U.S. Pat. No. 4,608,161 wherein a fuel heater structure is disposed in the filter head of the filter assembly. In this disclosure special structure is provided between the filter head and the spin-on filter element to displace fuel which might have been trapped in this location and which avoids significant fuel spillage upon element replacement.